Digital information to be communicated in communication systems operating in the asynchronous transfer mode, particularly in switching equipment or switching-oriented front-end equipment is communicated by packets having a fixed length, which are known as cells in the technical field. The cells cover 48 octets for the digital useful information to be communicated and 5 octets for a cell header in which is inserted the switching-oriented information for a virtual path in a communication network. The cells are predominantly formed in communication terminal equipment connected to the communication system and are communicated to the communication system. Alternatively, digital information communicated by the communication terminal equipment can be packeted into cells in the communication system.
Previously known methods for allocating switching-oriented resources of a communications system are based on statistical traffic behavior of the communication terminal equipment, whereby the switching-oriented resources are allocated to the cells or digital information incoming in the communication system in the sequence of their arrival for the purpose of an internal switching in the communication system. The switching-oriented resources represent those operating means that are provided for the temporary switching of the cells given, for example, dialed connections. The switching-oriented resources particularly encompass the central switching equipment and sub-switching equipment as well as multiplexing equipment of communication systems.
A communication relationship or connection between the communication terminal equipment via virtual routes or paths in a communication network operating in the asynchronous transfer mode is established with the assistance of known, standardized signaling procedures. A routing table is thereby provided for each of the communication systems lying in the virtual path. Path information defining the communication system input and output of the path that are calculated by the communication systems during the signaling procedure is inserted into these routing tables. The switching-oriented resources required for the respective connection are allocated in the communication systems on the basis of switching-oriented particulars such as average transmission rate or peak transmission rate that are signaled by the communication terminal equipment.
Given a temporary overload situation of a communication system, i.e., the scope of the switching-oriented resources of a communication system is not adequate in order to switch the incoming cells, those cells that cannot be immediately switched are intermediately stored in memory devices in a known way. However, a switching of the cells that is free of cell losses or free of disturbances is achieved with a somewhat greater delay. Given longer-duration overload situations, individual cells or cell groups are switched or discarded, for example according to a statistical method, i.e., are no longer transmitted. Such a statistical allocation of switching-oriented resources is known, for example, from the publication, IEEE International Conference on Communications, Conference Record Vol. 1, World Prosperity through Communications (1989), `A statistical band with allocation and usage monitoring algorithms for ATM-networks`, 13.5.1 through 13.5.8. Furthermore, it is known to implement the discarding of the cells dependent on an identifier for example, on a priority identifier. The cells having lower priorities are thereby discarded substantially more often than cells having higher priorities. In all of these known methods, at least individual cells are discarded, as a result whereof frequently disturbed transmissions are recognized and renewed transmission attempts are initiated in the transmission of data, for example file transfers, being initiated by the higher-ranking protocol levels in the communication terminal equipment. These disturbances in data transmission caused by the cell discarding ultimately lead to more and more repetitions of transmissions and to a further increase in the traffic load on the communication system involved therewith and, connected therewith, to constantly dropping usage rates of the transmission capacities. This means that a communication of digital information, particularly when there must be no data loss, is no longer possible in overload situations of communication systems operating in the asynchronous transfer mode due to constant repetitions and the resulting increased traffic load.